chore: back-end remove mvn for gradle

backend/.gitignore

@@ -0,0 +1,52 @@
+/target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+target
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbproject/public/
+/nbproject/project.properties
+/nbproject/project.xml
+
+### VS Code ###
+.vscode/
+
+### Gradle ###
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### Java ###
+*.class
+*.log
+*.ctxt
+.mtj.tmp/
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+### Spring Boot ###
+HELP.md